U.S. Pat. No. 4,853,202A disclosed a ETS-10 titanosilicate molecular sieve for the first time. In view of structure, the zeolite molecular sieves discovered before the ETS-10 titanosilicate molecular sieves, including aluminosilicate series (Y, β, ZSM-5, and others), aluminophosphate series (AlPO4-n), titanosilicate series (TS-1, TS-2) and the like, all have a skeleton formed of tetra-coordinate TO4 (T includes Si, Al, P, Ti, etc.) structures.
The ETS-10 titanosilicate molecular sieve is distinctly different from conventional zeolite in that its skeletal Ti is present completely in the form of a hexa-coordinate octahedral (TiO6)2− while the skeletal Si is still present in a tetra-coordinate structure (SiO4), and it has a channel structure of maximum 12-membered rings. In the skeleton of the ETS-10 titanosilicate molecular sieve, different (TiO6)2− octahedrons form a Ti—O—Ti chain structure known as the titanium chain by connecting opposite apexes via an oxygen bridge, and the four corners are connected with four (SiO4) tetrahedrons via oxygen bridges. Each (TiO6)2− octahedron has a charge number of −2 that needs to be balanced with positively charged alkali ions (normally Na+ and K+), and is thus endowed with an ion exchange property (M. W. Anderson, O. Terasaki, A. Philippou, et al. Structure of the microporous titanosilicate ETS-10. Nature, 1994, 367: 347-350). Hexacoordinate Ti has properties of TiO2, for example, those for photocatalysis, for acting as a hydrogenation catalyst carrier, etc.
A hydrothermal crystallization method is primarily used for ETS-10 titanosilicate molecular sieve synthesis, which comprises mixing a titanium source and a silicon source and carrying out hydrothermal crystallization at certain alkalinity in the presence of a mineralizer or a template in a closed container at a certain temperature to obtain a ETS-10 titanosilicate molecular sieve.
U.S. Pat. No. 4,853,202A has first disclosed a synthesis method for ETS-10 titanosilicate molecular sieves. The method published in this patent application employs a trivalent titanium compound, e.g. TiCl3, as the titanium source. Trivalent titanium sources are characterized in that they do not hydrolyze directly, but hydrolyze and precipitate only after being converted into tetravalent titanium, which will affect the ultimate synthesis efficiency. Furthermore, trivalent titanium sources are unstable, highly reducing, and instantly decomposed upon exposure to water or air, and stringent requirements are imposed on the operation in the synthesis where such titanium sources are used.
Lu Lv et al. (L. Lv, F. Su, X. S. Zhao, A reinforced study on the synthesis of microporous titanosilicate ETS-10. Microporous and Mesoporous Materials, 2004, 76: 113-122) systematically studied the impact of various titanium sources, including solid TiO2, TiF4, TiCl3 and (NH4)2F6Ti, on the synthesis, and proposed different mechanisms for synthesis of ETS-10 titanosilicate molecular sieves using TiCl3 and TiO2 respectively. Among them, the commercial product TiO2 with the code P25 used for synthesizing ETS-10 titanosilicate molecular sieves gives the best effect, but P25-type nanoscale TiO2 is expensive, has relatively high cost in synthesis, and thus is not suitable for industrial application.
Zhaoxia Ji et al. (Z. Ji, B. Yilmaz, J. Warzywoda, et al. Hydrothermal synthesis of titanosilicate ETS-10 using Ti(SO4)2. Microporous and Mesoporous Materials, 2005, 81(1-3): 1-10) studied various conditions for ETS-10 titanosilicate molecular sieve synthesis using Ti(SO4)2 as the titanium source. Si Hyun Noh et al. (S. H. Noh, S. D. Kim, Y. J. Chung, et al. The effects of (Na+K)/Na molar ratio and kinetic studies on the rapid crystallization of a large pored titanium silicate, ETS-10 using cost efficient titanium oxysulfate, TiOSO4 under stirring. Microporous and Mesoporous Materials, 2006, 88: 197-204) studied various conditions for ETS-10 titanosilicate molecular sieve synthesis using TiOSO4 as the titanium source, as TiOSO4 is cheap.
CN1724360A discloses a synthesis method for ETS-10 titanosilicate molecular sieves, wherein the ETS-10 titanosilicate molecular sieve is synthesized in the absence of templates, crystal seeds and F ions by using TiCl4 as the titanium source and a sodium silicate solution as the silicon source.